U.S. Pat. No. 4,266,049 teaches a process for converting a 3-(alkanoyloxy or carbamoyloxy)cephalosporin to the corresponding 3-iodomethyl cephalosporin with a trialkylsilyl iodide. This process requires separate blocking of the 4-carboxylic acid and 7-amino substituents prior to the reaction.
The present process permits the synthesis of 3-iodomethyl cephalosporins from a bis(trialkylsilyl)-7-amino-4-carboxylic acid starting material. Since separate blocking of the 7-amino and 4-carboxylic acid substituents is not necessary, the synthesis of 3-iodomethyl cephalosporins in fewer steps is now possible. Further, the present process permits the synthesis of the desired compounds in higher yields than previously possible. These advantages are significant when preparing large quantities of 3-iodomethyl cephalosporins which are intermediates for clinically active compounds. In addition, the present process permits the introduction of any desired acyl group at the 7-position of the cephalosporin ring without separate blocking or deblocking steps.